"There is no indication that this incident is related to terrorism, although we are not ruling anything out," Army commander Lt General Mark Milley was quoted as saying.

The suspect has been now identified by the authorities as Specialist Ivan Lopez.

The CNN quoted an FBI official as saying that the suspect's wife is cooperating with the law enforcement officials.

The US Army had earlier refused to make public the name of the gunman until his family was notified.

A US Army spokesman said that Lopez had served in Iraq and was suffering from mental problems like depression and anxiety and was also receiving treatment. He was said to be undergoing the diagnosis for Post-Traumatic Stress Disorder (PTSD), but he hadn't been confirmed having that disorder.

"He was not diagnosed, as of today, with PTSD," said the US Army commander Miley.

Miley added that Lopez used a .45 caliber Smith and Wesson semiautomatic pistol to carry out the shooting spree and that the pistol was not registered.

"If you have weapons and you're on base, it's supposed to be registered on base...This weapon was not registered on base," the commander said.

The authorities are yet not clued about the motive behind the shooting but the US commander hinted that there might have been an argument that culminated in the gunman's murderous outburst.

"There are initial reports there may have been an argument in one of the unit areas," Lt. Gen Mark Milley said.

The gunman's background was being looked into to check for any "criminal or psychiatric history, his experiences in combat", said the Commander.

Expressing regret over the incident, US President Barack Obama said that he was “heartbroken” over the incident.

“Any shooting is troubling. Obviously this reopens the pain of what happened at Fort Hood five years ago...We’re heartbroken that something like this might have happened again,”said Obama.

The incident took pace 4:30 pm local time when the soldier drove to two buildings and started firing before the military police stopped him. He then killed himself using a .45 caliber Smith and Wesson semiautomatic pistol.

Fort Hood was immediately put on lockdown and officers carried out a building to building search for the shooter.

The shooting incident at Fort Hood base brings back the tragic memories of 2009 when an Army psychiatrist Maj Nidal Hassan had killed 13 soldiers on Nov 5, 2009.